Granular activated carbons and activated carbon fibers are known as exhibiting adsorptivity and desorptivity for various substances. In particular, the activated carbon fiber is fibrous and utilized as it is or molded into appropriate form before use. The activated carbon fiber is widely used in various adsorptive materials such as an adsorbent, a water purifier, a deodorant and a deodorizing filter, a catalyst carrier, etc.
The known activated carbon fibers include not only organic activated carbon fibers prepared from rayon, polyacrylonitrile, phenolic resin and the like as starting materials but also pitch-based activated carbon fibers obtained by spinning pitch, for example, an optically isotropic pitch to thereby obtain pitch fibers, infusibilizing the pitch fibers and carbonizing/activating the infusibilized fibers.
It is believed that the pore structure, pore size, pore density and/or pore distribution of the activated carbon fiber is a factor of utmost importance for causing the activated carbon fiber to possess such a large specific surface area that the adsorptive and desorptive functions of the activated carbon fiber are fully exerted. Accordingly, with respect to the production of the activated carbon fiber from an optically isotropic pitch, various proposals have been made regarding the regulation of conditions in the production of the optically isotropic pitch, in the spinning and infusibilization of the pitch fiber in the carbonization and activation. In this connection, reference is made to Japanese Patent Laid-Open Publication Nos. 61(1986)-295218, 5(1993)-209322, 6(1994)-17321, 6(1994)-272117, 6(1994)-272118, 6(1994)-306710 and 7(1995)-145516.
However, the conventional activated carbon fiber has the problem that its bulk density is too low to make total amount of adsorbed substances sufficiently high even if its adsorbing amount of substances per weight is high with the result that the adsorptive capacity of the activated carbon fiber cannot be fully utilized.
Thus, molding of the activated carbon fibers with the use of a binder or the like has been tried for improving the packing density of the activated carbon fibers. However, the resultant molded article of activated carbon fibers suffer from deterioration of the adsorptivity of the activated carbon fibers per se because of, for example, the clogging of pores of the activated carbon fibers by the binder or the like, so that a high adsorptivity cannot be attained.
The inventors have made extensive and intensive studies in these current circumstances. As a result, it has been found that, in the process for producing the activated carbon fibers from the optically isotropic pitch, the desired activated carbon fiber molding of high bulk density can be provided by shaping the infusibilized fibers under a load and activating the shaped fibers. The present invention has been completed on the basis of the above finding.